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Commit c463ba45 authored by Christopher Ferris's avatar Christopher Ferris
Browse files

Add error reporting mechanism for failing Unwind. 

Remove the logging of an error if a thread disappears before the unwind
can begin. This can happen, so allow the caller to determine if this
is really a problem worth logging.

Bug: 27449879

(cherry picked from commit 206a3b97)

Change-Id: If9e7cfeb6eb7b122679a734c1a9eacee8354ef18
parent 01d76eb1

debuggerd/backtrace.cpp

+2 −1
Original line number Diff line number Diff line
@@ -91,7 +91,8 @@ static void dump_thread(log_t* log, BacktraceMap* map, pid_t pid, pid_t tid) { 
  if (backtrace->Unwind(0)) {

    dump_backtrace_to_log(backtrace.get(), log, "  ");

  } else {

    ALOGE("Unwind failed: tid = %d", tid);

    ALOGE("Unwind failed: tid = %d: %s", tid,

          backtrace->GetErrorString(backtrace->GetError()).c_str());

  }

}

include/backtrace/Backtrace.h

+24 −0
Original line number Diff line number Diff line
@@ -34,6 +34,24 @@ typedef uint64_t word_t; 
typedef uint32_t word_t;

#endif



enum BacktraceUnwindError : uint32_t {

  BACKTRACE_UNWIND_NO_ERROR,

  // Something failed while trying to perform the setup to begin the unwind.

  BACKTRACE_UNWIND_ERROR_SETUP_FAILED,

  // There is no map information to use with the unwind.

  BACKTRACE_UNWIND_ERROR_MAP_MISSING,

  // An error occurred that indicates a programming error.

  BACKTRACE_UNWIND_ERROR_INTERNAL,

  // The thread to unwind has disappeared before the unwind can begin.

  BACKTRACE_UNWIND_ERROR_THREAD_DOESNT_EXIST,

  // The thread to unwind has not responded to a signal in a timely manner.

  BACKTRACE_UNWIND_ERROR_THREAD_TIMEOUT,

  // Attempt to do an unsupported operation.

  BACKTRACE_UNWIND_ERROR_UNSUPPORTED_OPERATION,

  // Attempt to do an offline unwind without a context.

  BACKTRACE_UNWIND_ERROR_NO_CONTEXT,

};



struct backtrace_frame_data_t {

  size_t num;             // The current fame number.

  uintptr_t pc;           // The absolute pc.
@@ -127,6 +145,10 @@ public: 


  BacktraceMap* GetMap() { return map_; }



  BacktraceUnwindError GetError() { return error_; }



  std::string GetErrorString(BacktraceUnwindError error);



protected:

  Backtrace(pid_t pid, pid_t tid, BacktraceMap* map);
@@ -145,6 +167,8 @@ protected: 
  bool map_shared_;



  std::vector<backtrace_frame_data_t> frames_;



  BacktraceUnwindError error_;

};



#endif // _BACKTRACE_BACKTRACE_H

libbacktrace/Backtrace.cpp

+21 −0
Original line number Diff line number Diff line
@@ -148,3 +148,24 @@ Backtrace* Backtrace::Create(pid_t pid, pid_t tid, BacktraceMap* map) { 
    return new UnwindPtrace(pid, tid, map);

  }

}



std::string Backtrace::GetErrorString(BacktraceUnwindError error) {

  switch (error) {

  case BACKTRACE_UNWIND_NO_ERROR:

    return "No error";

  case BACKTRACE_UNWIND_ERROR_SETUP_FAILED:

    return "Setup failed";

  case BACKTRACE_UNWIND_ERROR_MAP_MISSING:

    return "No map found";

  case BACKTRACE_UNWIND_ERROR_INTERNAL:

    return "Internal libbacktrace error, please submit a bugreport";

  case BACKTRACE_UNWIND_ERROR_THREAD_DOESNT_EXIST:

    return "Thread doesn't exist";

  case BACKTRACE_UNWIND_ERROR_THREAD_TIMEOUT:

    return "Thread has not repsonded to signal in time";

  case BACKTRACE_UNWIND_ERROR_UNSUPPORTED_OPERATION:

    return "Attempt to use an unsupported feature";

  case BACKTRACE_UNWIND_ERROR_NO_CONTEXT:

    return "Attempt to do an offline unwind without a context";

  }

}

libbacktrace/BacktraceCurrent.cpp

+20 −2
Original line number Diff line number Diff line
@@ -24,6 +24,8 @@ 
#include <ucontext.h>

#include <unistd.h>



#include <stdlib.h>



#include <string>



#include <backtrace/Backtrace.h>
@@ -65,9 +67,11 @@ size_t BacktraceCurrent::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) { 
bool BacktraceCurrent::Unwind(size_t num_ignore_frames, ucontext_t* ucontext) {

  if (GetMap() == nullptr) {

    // Without a map object, we can't do anything.

    error_ = BACKTRACE_UNWIND_ERROR_MAP_MISSING;

    return false;

  }



  error_ = BACKTRACE_UNWIND_NO_ERROR;

  if (ucontext) {

    return UnwindFromContext(num_ignore_frames, ucontext);

  }
@@ -138,11 +142,19 @@ bool BacktraceCurrent::UnwindThread(size_t num_ignore_frames) { 
    BACK_LOGE("sigaction failed: %s", strerror(errno));

    ThreadEntry::Remove(entry);

    pthread_mutex_unlock(&g_sigaction_mutex);

    error_ = BACKTRACE_UNWIND_ERROR_INTERNAL;

    return false;

  }



  if (tgkill(Pid(), Tid(), THREAD_SIGNAL) != 0) {

    BACK_LOGE("tgkill %d failed: %s", Tid(), strerror(errno));

    // Do not emit an error message, this might be expected. Set the

    // error and let the caller decide.

    if (errno == ESRCH) {

      error_ = BACKTRACE_UNWIND_ERROR_THREAD_DOESNT_EXIST;

    } else {

      error_ = BACKTRACE_UNWIND_ERROR_INTERNAL;

    }



    sigaction(THREAD_SIGNAL, &oldact, nullptr);

    ThreadEntry::Remove(entry);

    pthread_mutex_unlock(&g_sigaction_mutex);
@@ -183,8 +195,14 @@ bool BacktraceCurrent::UnwindThread(size_t num_ignore_frames) { 
      BACK_LOGW("Timed out waiting for signal handler to indicate it finished.");

    }

  } else {

    // Check to see if the thread has disappeared.

    if (tgkill(Pid(), Tid(), 0) == -1 && errno == ESRCH) {

      error_ = BACKTRACE_UNWIND_ERROR_THREAD_DOESNT_EXIST;

    } else {

      error_ = BACKTRACE_UNWIND_ERROR_THREAD_TIMEOUT;

      BACK_LOGE("Timed out waiting for signal handler to get ucontext data.");

    }

  }



  ThreadEntry::Remove(entry);

libbacktrace/BacktraceOffline.cpp

+3 −0
Original line number Diff line number Diff line
@@ -129,9 +129,11 @@ static unw_accessors_t accessors = { 
bool BacktraceOffline::Unwind(size_t num_ignore_frames, ucontext_t* context) {

  if (context == nullptr) {

    BACK_LOGW("The context is needed for offline backtracing.");

    error_ = BACKTRACE_UNWIND_ERROR_NO_CONTEXT;

    return false;

  }

  context_ = context;

  error_ = BACKTRACE_UNWIND_NO_ERROR;



  unw_addr_space_t addr_space = unw_create_addr_space(&accessors, 0);

  unw_cursor_t cursor;
@@ -139,6 +141,7 @@ bool BacktraceOffline::Unwind(size_t num_ignore_frames, ucontext_t* context) { 
  if (ret != 0) {

    BACK_LOGW("unw_init_remote failed %d", ret);

    unw_destroy_addr_space(addr_space);

    error_ = BACKTRACE_UNWIND_ERROR_SETUP_FAILED;

    return false;

  }

  size_t num_frames = 0;